/etc/motd and /etc/issue  

Bash offers an option to include messages in the /etc/motd and the /etc/issue files. Messages in /etc/motd display after a user has successfully logged in to a shell.用户登录shell之后显示的信息 (Notice that users in a graphical environment do not see its contents after a graphical login.图形登录界面看不到这个信息提示) Using /etc/motd can be a convenient way for system administrators to inform users. 

Another way to send information to users is by using /etc/issue. The contents of this file display before the user logs in. This provides an excellent means of specifying specific login instructions to users who are not logged in yet. 这个是在用户登录之前显示的信息。